The present invention relates to a plasma display panel (hereafter abbreviated to PDP), and especially to a PDP in which the strength of luminescence per unit of injected energy, that is, the discharge efficiency, is improved, and which can display a bright and clear image with low consumption of power.
The AC surface-discharge type PDP with a three electrode structure, such as that disclosed in Japanese Patent Application Laid-Open Hei 5-307935, is a typical conventional PDP. This type of PDP includes a top face glass substrate and a back face glass substrate. Inside the top face glass substrate, plural pairs of X sustain electrodes and Y sustain electrodes are formed, each electrode consisting of a transparent electrode and a bus electrode. These electrodes are named X electrodes and Y electrodes, or the sustain electrodes in general. The sustain electrodes are covered with a dielectric material layer made of various kinds of material. Foundations and a plurality of address electrodes are situated on the back face glass substrate, and are covered with a dielectric material and a fluorescent material. Each address electrode is partitioned by two partition parts. The top and back face glass substrates are assembled so that the gap between the two substrates is kept constant, and the discharge space between the substrates is filled with a mixed gas whose main component is a rare gas, such as Ne, Xe, etc. Xe is a gas which radiates ultraviolet rays for making the fluorescent material emit light, and Ne is a buffering gas. Thus, when a discharge for displaying an image occurs, visible light is radiated from the fluorescent material via the top face glass substrate. A screen is composed of many pixels, and each pixel includes three discharge cells in which red, green, and blue fluorescent substances are employed, respectively. A PDP with the above structure is called a three-electrode surface-discharge type PDP.
In a typical method of driving the three-electrode surface-discharge type PDP, the PDP is driven by a drive frame of 16.7 ms, which is divided into a plurality of subfields. Each subfield is composed of a reset discharge period in which wall charges in all cells are extinguished; an addressed-cell discharge period in which wall charges are formed only in cells on which image data are to be displayed according to a display control signal; and a sustain discharge period in which the discharge in the addressed cell is maintained according to the image data while using the formed wall charges. A multi-gradation display is implemented by changing the length of the sustain discharge period in each subfield, and a full-color display is realized by combining discharges in three cells in which red, green, and blue fluorescent substances are applied, respectively.
Another type of conventional PDP, that is, an AC driven subrib type PDP of two-electrode structure, is disclosed, for example, in Japanese Patent Application Laid-Open Hei 5-41165. In this structure, two sustain electrodes are arranged perpendicular to each other, so as not to contact each other, in the dielectric material layer in the back plate. There are no address electrodes, and the addressed discharge is generated between the pair of sustain electrodes. Each cell is partitioned by barrier ribs, and fluorescent material is applied on the barrier ribs. Further, other barrier subribs lower than the above barrier ribs, project to the discharge space from the back plate, and fluorescent material is also applied on these barrier subribs. In the same manner as the three-electrode surface-discharge type PDP, the top and back face glass substrates are assembled so that the gap between these substrates is kept constant, and the discharge space between the substrates is filled with a mixed gas whose main component is a rare gas, such as Ne, Xe, etc. When the discharge for image-displaying occurs, visible light is radiated from the fluorescent material through the front plate. This structure is designed to improve the brightness by elongating the discharge path and increasing the surface area of the fluorescent material. A PDP having the above structure is simply referred to as a two-electrode subrib type PDP.
Since there is no address electrode in the two-electrode subrib type PDP, its drive method is different from that of the three-electrode surface-discharge type PDP. However, the drive method of the two-electrode subrib type PDP is not described in Japanese Patent Application Laid-Open Hei 5-41165. Further, the two-electrode subrib type PDP has not come into practical use as yet.
On the other hand, although the three-electrode surface-discharge type PDP has come into practical use, and has been manufactured already, improvement of the brightness and reduction of the power consumption have been important objectives for this type of PDP. That is, the main design objective of this type of PDP is to improve the discharge efficiency (the ratio of the energy emitted as ultraviolet rays to the energy injected into a cell).
An object of the present invention is to provide a PDP which can stably display an image with high brightness, high gradation, and low power consumption.
Further, another object of the present invention is to improve the discharge efficiency of a PDP.
To achieve the foregoing objects of this invention, the present invention provides a plasma display panel comprising: a first substrate including a first dielectric material layer which covers a plurality of address electrodes; back face barrier ribs, each of which is located between two neighboring address electrodes; a fluorescent material layer which covers the back face barrier ribs and the first dielectric material layer; and a second substrate including plural pairs of X sustain electrodes and Y sustain electrodes, which are arranged so as to cross at right angles relative to the address electrodes; and a second dielectric material layer which covers the sustain electrodes. The first substrate is arranged opposite to the second substrate via a discharge space which is filled with a gas for radiating ultraviolet rays, to make the fluorescent material layer emit light, and a buffer gas, and the thickness of the second dielectric layer in the second substrate is set larger, at a portion between the X and Y sustain electrodes, than that at other portions in the second dielectric layer, that is, a dielectric material barrier rib of appropriate height is provided in a region between each pair of X and Y sustain electrodes. By forming this dielectric material barrier rib, since it is possible to avoid using the region between the X and Y sustain electrodes, in which the electric field is very strong, it is possible to effectively make the electrode field more uniform. Further, it is desirable to use a coplanar electrode configuration, obtained by bending a discharge cell composed of a pair of electrodes opposite to each other at its middle position so that the pair of electrodes are arranged on the same plane. In this coplanar configuration, since it is possible to take advantage of the discharge of opposed electrodes in the sustain discharge, improvement of the discharge efficiency becomes possible by increasing the partial pressure of gas for radiating ultraviolet rays without increasing the operating voltage of the discharge cell.
It is a known fundamental physical phenomenon that the discharge efficiency is improved as the partial pressure of gas for radiating ultraviolet rays is increased. However, if an attempt is made to improve the discharge efficiency in the conventional three-electrode surface discharge type PDP by simply increasing the partial pressure of such gas, it will be found that the operating voltage in the sustain discharge exceeds a practical range.
Also, it is known that if the conditions of the partial pressure of gas for radiating ultraviolet rays; the discharge-gap length; the voltage applied between the electrodes; etc., are the same, then the operating voltage in the sustain discharge between a pair of electrodes disposed opposite to each other (hereafter referred to as discharge in the opposed electrodes) is lower than the operating voltage in the sustain discharge between a pair of electrodes arranged in the same plane (hereafter referred to as surface discharge in the coplanar electrodes). Since the surface discharge in the coplanar electrodes is adopted in the conventional three-electrode surface discharge type PDP, the operating voltage is comparatively high.
Thus, if the advantage of the discharge in the opposed electrodes can be incorporated into the three-electrode surface discharge type PDP in accordance with the present invention, it will improve the discharge efficiency by increasing the partial pressure of gas for radiating ultraviolet rays without increasing the operating voltage.